Field of the Invention
The present invention relates to a recording apparatus employing a magnetic linear encoder, and more particularly to a serial recording apparatus provided with a magnetic linear encoder along the moving direction of the carriage.
Related Background Art
The serial recording apparatus effects recording (printing) operation by causing a carriage which supports a printing head constituting recording means to effect a lateral scanning motion to a recording medium or a recording sheet, and, in such apparatus, the density of the obtained record becomes uneven if the speed of the carriage fluctuates for some reasons. Particularly in the color printer, such fluctuation in the carriage speed is a problem because the registration of the colors is aberrated.
For avoiding these drawbacks, there is conventionally known a configuration of detecting the amount of movement of the carriage supporting the recording means with respect to the main body of the recording apparatus and effecting the recording operation by the recording means in synchronization with the movement of the carriage, based on the result of said detection. More specifically, the scale of the linear encoder is fixed on said main body while the detecting unit of the linear encoder is loaded on the carriage which moves relative to said scale, and the recording signal is generated in synchronization with the amplified output signal of said detecting unit, whereby the uneven print density and the aberration in color registration are avoided.
In such recording apparatus there has principally been employed the optical linear encoder in which translucent portions and opaque portions alternately formed on a film or a thin plate are detected by a photodiode or a phototransistor, but such optical linear encoder is very expensive when a high resolving power is looked for, and is susceptible to dusts, such as those from recording paper, inevitable in the recording apparatus. In fact, such optical linear encoder is practically unapplicable to the ink jet recording apparatus or the like of a resolving power in the order of 360 dot/inch.
For avoiding these drawbacks, the magnetic linear encoder, disclosed in the Japanese Patent Publication No. 62-57929, has reached the stage of practical application. The scale of said magnetic linear encoder has magnetic anisotropy in the vertical direction, and a predetermined portion of said scale is magnetized with a constant pitch and utilized for generating the carriage control signal, triggering the driving of the recording head or the position detection.
FIG. 1 is a schematic view of a recording apparatus employing the conventional magnetic linear encoder. A recording head 1, integrally containing an ink jet head and an ink tank, is preferably detachably mounted on the recording apparatus and is replaced by a new head when the ink in the ink tank is exhausted.
A carriage 2, supporting the recording head 1, is provided with a pin (not shown) engaging with a spiral groove of a lead screw 3 which is rotated, through a transmission mechanism (not shown), by the forward or reverse rotation of a carriage motor (not shown), and is reciprocated in the directions a, b by the rotation of said lead screw 3. The magnetized portion of a scale 11 is read by a magnetic head, provided with an MR (magnetic resistance) device (not shown in FIG. 1 ).
A transport roller 4 advances a recording sheet 5 in a direction c, intermittently at the recording operation. The magnetic head 12 is provided, for extracting the output signal of the MR device, with a flexible circuit board 13, which is connected to a circuit board 6 on the carriage 2, by connecting a contact portion 14 with a connector (not shown).
The magnetic head 12 is integrally constructed with a housing 12'.
Such conventional configuration has however been associated with the following drawbacks because the scale of the linear encoder is merely magnetized in continuous manner with a single pitch:
(1) As the position signal can be obtained only with a single pitch, there are required increased hardware such as frequency dividers and counters and increased burden on software in order to achieve two or more recording densities on the same recording apparatus; PA1 (2) The cost of the linear encoder becomes high since a linear encoder cannot be used in the recording apparatus of different recording densities; and PA1 (3) An inexpensive recording apparatus with a high effective recording speed cannot be realized since a trigger signal for controlling the apparatus cannot be obtained at an arbitrary position, without an increase in the hardware such as timer and an increase in the burden of the software.
Also in the conventional linear encoder, the scale is often shaped as a rod with a circular cross section, and is longitudinally magnetized in a part of the external periphery thereof. Such scale involves considerable difficulty in the mounting on the main frame of the recording apparatus, as the magnetized portion of the scale has to be positioned in a certain direction opposed to the magnetic head.
Furthermore, in the above-mentioned conventional example, the magnetic linear encoder is magnetized with a constant pitch only, for the purpose of generating the position signal for recording, the administrative information such as the serial number of the apparatus has to be recorded on the package or the outer casing of the apparatus, and these facts have lead to the inferior assembling efficiency and the increased cost.
Also the data specific to each unit of the apparatus, if stored in a ROM, will lead to a significant increase of cost, because the ROM has to be modified in the content for each unit and cannot be prepared by a single mask.
The conventional magnetic linear encoder, being generally magnetized with a single pitch as explained above, is excellent for relative position control but is unable to detect so-called absolute position. Such magnetic linear encoder is unable to detect, for example, the absolute position of the carriage home position, the absolute position for capping of the recording head for preventing the evaporation of ink therefrom in order to maintain the satisfactory printing ability, or the absolute position for a recovery system for removing the substance deposited on the head surface. For this reason, in the conventional recording apparatus, the magnetic linear encoder is employed in the ordinary operations for example at the recording but the absolute positions required for other functions are detected by microswitches and a photointerruptor consisting of a photocoupler and a shield plate mounted on the carriage, or by such microswitches and the counting of the pulses from the stepping motor for driving the carriage.